MOS field-effect transistors with very thin silicon dioxide based gate dielectrics may experience unacceptable gate leakage currents. Forming the gate dielectric from certain high-k dielectric materials, instead of silicon dioxide, can reduce gate leakage. Such a dielectric may not, however, be compatible with polysilicon—the preferred material for making the device's gate electrode.
When high-k films comprise an oxide formed using a metal halide precurser (e.g., a metal chloride), they may contain significant amounts of impurities (e.g., residual chlorine), which may adversely affect the electrical properties of a device that includes that film. In addition, an oxide based high-k film may manifest oxygen vacancies at random surface sites. When the device's gate electrode comprises polysilicon, a silicide may form where such vacancies occur. The silicide's presence may alter the electrode's workfunction or cause the device to short through the dielectric.
Accordingly, there is a need for an improved process for making a semiconductor device that includes a high-k gate dielectric. There is a need for such a process that removes a substantial amount of unwanted impurities from the high-k film prior to forming a polysilicon gate electrode on its surface. There is also a need for such a process that eliminates (or at least minimizes) silicide formation, when a polysilicon gate electrode is formed on the high-k film. The method of the present invention provides such a process.